The long-term goal of this project is to describe and characterize in detail the pal-1 transcriptional networks that specify and pattern the C blastomere lineage in the early C. elegans embryo. The invariant development of C. elegans allowed Sulston and co-workers to describe the cell lineage of normal development. This description has proven invaluable in the analysis of developmental pathways and mechanisms. The sequencing of the nematode genome has provided the means to monitor the expression levels of all predicted genes using oligonucleotide microarrays. Here, we propose to combine these descriptive technologies and then use the powerful molecular and genetic tools available in C. elegans to characterize the transcriptional program that specifies the fate of an early embryonic blastomere.pal-1 activity is necessary and sufficient to specify the C lineage. We hypothesize thatpal-1 controls a robust gene network, the regulatory structure of which will be determined by identifying and characterizing many pal-1 target genes, particularly their upstream control regions (Aim 1). Furthermore, we hypothesize that the developmental robustness of this network is due primarily to functional redundancy of homologous target genes, but depends as well on compensating interactions within the regulatory network among non-homologous genes. RNAi of multiple genes (Aim 3) will reveal functional redundancy among homologs. To test for developmental robustness conferred by compensating regulatory interactions we will first use mathematical modeling (Aim 2) to predict the gene network architecture to identify specific non-homologous genes for similar analysis (Aim 3). This analysis, although limited to those genes that are transcriptional targets of pal-1 activity, is the necessary first step to a complete description of the activity of a master regulator.